The present invention is directed to a bicycle shifting device which operates a shifting mechanism via a shifter cable, and specifically concerns a device in which a take-up body that takes up the shifter cable is caused to rotate in the take-up direction by means of a first shift lever which freely returns to a home position, and is caused to rotate in the pay-out direction by means of a second shift lever which freely returns to a separate home position.
A bicycle shifter operating device equipped with first and second shift levers such as those described above is known (for example) from Japanese Patent Application Kokai No. 4-183696. In this shifter operating device, the first shift lever and the second shift lever can pivot about a common pivoting axis wherein the operating direction of the first shift lever is clockwise and the operating direction of the second shift lever is counterclockwise. The first shift lever is arranged so that it can be operated by the thumb of the hand gripping the handlebar, and the second shift lever is arranged so that it can be operated by the index finger of the hand gripping the handlebar. In such shifting devices the first and second levers typically pivot about an axis that is perpendicular to the handlebar.
During high performance riding on rough terrain it is often desirable to keep the hands as firmly positioned on the handlebars as possible. However, when using the above shifting devices it is necessary to remove the index finger from the handlebar in order to operate the second shift lever. Some cyclists find the movement of the index finger in such cases undesirable.
Some shifting devices are constructed as shown in U.S. Pat. No. 4,900,291 wherein the shifting operation is performed by rotating a sleeve mounted coaxially with the handlebar. Unfortunately, if the hand is maintained in position around the sleeve while riding there is a risk of unintended shifting when encountering rough terrain. If the hand is ordinarily kept in position on the rigid portion of the handlebar, then the entire hand must be removed from the handlebar to grasp the sleeve during shifting, which is even more undesirable. Thus, there is a need for a shifting device which allows the hand to be firmly positioned on the handlebar at all times with a minimum of movement during shifting.
Another ergonomic consideration of shifting devices is the sensory feedback provided by the shifting device. Some cyclists prefer a shifting device which provide very different sensory feedback between the upshifting and downshifting operations. For those cyclists a shifting device with two pivoting levers does not provide sufficient sensory difference between the upshifting and downshifting operation, since both levers pivot. The same is true with shifting devices constructed with a rotating sleeve, since both upshifting and downshifting is performed by rotating the sleeve.
A bicycle shifter operating device in which the first shift lever is operated by pivoting and the second shift lever is operated by means of a button in order to achieve a clear sensory difference between the shifter cable take-up operation and the shifter cable pay-out operation is known from British Patent Disclosure No. 2,169,065 (corresponding to Japanese Patent Application Kokai No. 61-222889). In this shifter operating device, a pivoting lever is used when the take-up body is to be rotated in the direction which takes up the shifter cable. When the take-up body is to be rotated in the direction which pays out the shifter cable (using the driving force of a return spring), the cable is returned one speed at a time by means of a button-operated sliding pawl. Here, the shifter cable take-up operation is accomplished by a pivoting action, while the shifter cable pay-out operation is accomplished by a sliding action. Accordingly, there is a clear sensory difference between the two operations. Unfortunately, because of structural limitations, the pivoting lever and the button-operated part must be installed in completely different locations. Accordingly, it is difficult to perform both shifting operations using the fingers of the hand gripping the handlebar without undesirable movement of the hand.
Yet another ergonomic consideration is the placement of the finger contacting portions of the shift levers. When a shift lever is to be operated by the thumb, the shift lever should be placed in a position that does not require awkward movement of the thumb. This is especially true when separate shift levers are provided for upshifting and downshifting. Some riders prefer thumb operated shift levers to be located at the approximate plane of the palm. Unfortunately, the approximate plane of the palm usually corresponds to the location of the handlebar, and it is not feasible to mount conventional shift levers in front of the handlebar. That is because conventional shift levers require a relatively large swing angle to operate, and it would be necessary to mount the lever a great distance forward of the handlebar to prevent the lever from striking the handlebar during operation. This, in turn, would destroy the ergonomic positioning of the lever.